Hip replacement in computer-assisted surgery

ABSTRACT

A system for calculating a position and orientation of an acetabular cup in computer-assisted surgery comprises a first trackable reference secured to a pelvis, with a frame of reference being associated with the first trackable reference. A device is positionable between a femoral neck and the acetabulum of the pelvis in a known relation, the device having a second trackable reference. Sensors track the trackable references for position and orientation. A position/orientation calculator calculates a position and orientation of the frame of reference and of the device and for determining an orientation of the neck axis with respect to the frame of reference from the known relation at a desired position of the femur. An implant position/orientation calculator provides cup implanting information with respect to the orientation of said neck axis as a function of the tracking for position and orientation of at least the first trackable reference.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of U.S. patent application Ser. No.12/249,393 filed on Oct. 10, 2008, which claims priority on U.S.Provisional Patent Application No. 60/978,875, filed on Oct. 10, 2007.

FIELD OF THE APPLICATION

The present application relates to total hip-replacement surgery usingcomputer-assisted surgery systems and, more particularly, to a device,system and method for effecting total hip-replacement surgery.

BACKGROUND OF THE ART

Computer-assisted surgery (CAS) systems assist surgeons in differenttypes of surgery like neurosurgery, total hip replacement (THR) andtotal knee replacement (TKR). Each of these surgeries presents numerousmethods following different sequences of steps.

In THR, the patient can be positioned on his/her back or on his/her sideduring the surgery. Also, the surgeon can start either by working on thefemoral head or on the acetabulum. Surgeons commonly start a THR byfirstly working on the acetabulum, and thus by resurfacing theacetabulum to insert an acetabular cup implant. In the event that thecup is installed prior to the femoral implant being implanted, there area few difficulties if the cup is not properly installed at the firsttry. If it isn't properly installed, the surgeon may remove the cup andreposition it, which can prove difficult without damaging the bone ofthe pelvis. Alternatively, the surgeon may compensate for themisalignment when installing the femoral implant. If the femoral andacetabular cup implants are misaligned, there are greater risks ofdislocation of the femur, or impingement between the femoral implantneck and the acetabular cup or the pelvis.

When compared to the femoral implant, there is a greater range ofpossible positions/orientations associated with the implanting of anacetabular cup. It would be desirable to provide a method for selectingan orientation of the acetabular cup once the femoral implant isimplanted, to lessen the risk of misalignment.

SUMMARY OF THE APPLICATION

It is therefore an aim of the present application to provide a novelmethod for performing hip replacement surgery using a computer-assistedsurgery system.

It is a further aim of the present application to provide a trackablehip-joint device to digitize a projected femoral neck axis.

It is a further aim of the present application to provide a novelcomputer-assisted surgery system to perform total hip replacement.

Therefore, in accordance with the present application, there is provideda device for digitizing a femoral neck axis of with respect to a pelvicframe of reference in computer-assisted surgery, comprising: trackablemember trackable for position and orientation by a computer-assistedsurgery system; a body connected to the trackable member, the bodyhaving an interface portion adapted to be releasably coupled to a neckof one of an implanted femoral implant and a provisional in a knownrelation, and a bone interface portion adapted to be positioned againsta pelvis such that the body of the device interrelates the implantedfemoral implant or provisional to the pelvis, the neck axis of thefemoral implant or provisional being calculable thereat with respect tothe pelvic frame of reference as a function of the known relation and ofthe position and orientation of the trackable member.

Further in accordance with the present application, there is provided amethod of doing surgical treatment in computer-assisted surgery forguiding an operator in inserting a cup implant of a hip joint implantinto an acetabulum, comprising: positioning a trackable reference on apelvis, the trackable reference being trackable in space for positionand orientation so as to define a frame of reference; inserting any oneof a provisional and a femoral implant into a femur; digitizing a neckaxis of the provisional or femoral implant with respect to the frame ofreference; and inserting the cup implant into the acetabulum byobtaining cup implanting information with respect to the orientation ofsaid neck axis as a function of the tracking for position andorientation of the trackable reference.

Still further in accordance with the present application, obtaining cupimplanting information comprises tracking an orientation of reameraltering the acetabulum.

Still further in accordance with the present application, obtaining cupimplanting information comprises tracking an orientation of the cupimplant being implanted.

Still further in accordance with the present application, the methodcomprises reaming the acetabulum prior to digitizing the neck axis.

Still further in accordance with the present application, digitizing theneck axis comprises coupling the neck of the provisional or femoralimplant and the acetabulum with a tracked device, and orienting thefemur to a desired posture.

Still further in accordance with the present application, digitizing theneck axis comprises orienting the femur to a desired posture.

Still further in accordance with the present application, doing surgicaltreatment is performed on a bone model or a cadaver.

Still further in accordance with the present application, there isprovided a system for calculating a position and orientation of anacetabular cup in computer-assisted surgery, comprising: a firsttrackable reference secured to a pelvis, with a frame of reference beingassociated with the first trackable reference; a device positionablebetween a femoral neck and the acetabulum of the pelvis in a knownrelation, the device having a second trackable reference; sensors fortracking the trackable references for position and orientation; aposition/orientation calculator for calculating a position andorientation of the frame of reference and of the device and fordetermining an orientation of the neck axis with respect to the frame ofreference from the known relation at a desired position of the femur;and an implant position/orientation calculator for providing cupimplanting information with respect to the orientation of said neck axisas a function of the tracking for position and orientation of at leastthe first trackable reference.

Still further in accordance with the present application, the systemcomprises a reamer for reaming the acetabulum of the pelvis, the reamerhaving another trackable reference such that the cup implantinginformation is calculated as a function of the orientation of thereamer.

Still further in accordance with the present application, the systemcomprises another trackable reference removably connected to theacetabular cup such that the cup implanting information is calculated asa function of the orientation of the acetabular cup.

Still further in accordance with the present application, the devicecomprises a body connected to the second trackable reference, the bodyhaving an interface portion adapted to be releasably coupled to a neckof an implanted femoral implant or provisional in the known relation,and a bone interface portion adapted to be positioned into theacetabulum such that the body of the device interrelates the implantedfemoral implant to the pelvis.

Still further in accordance with the present application, the cupimplanting information comprises anteversion angle, offset angle, limblength discrepancy, range of motion data, visal displays of an axis withrespect to a pelvic image.

Still further in accordance with the present application, the desiredposture comprises the patient in a regular lying posture.

Still further in accordance with the present application, theposition/orientation calculator comprises a model of the device, and theknown relation comprises the model of the device.

Still further in accordance with the present application, the femoralneck is the femoral neck of any one of a femoral implant andprovisional.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flowchart illustrating a method for performing hipreplacement using a CAS system in accordance with a first embodiment ofthe present application;

FIG. 2 is a schematic view of a trackable hip-joint device in accordancewith a second embodiment of the present application;

FIG. 3 is a schematic view of the trackable hip-joint device of FIG. 2as used during hip-replacement surgery; and

FIG. 4 is a block diagram illustrating a computer-assisted surgerysystem in accordance with another embodiment of the present application,for performing hip-replacement surgery.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, a flowchart illustrating a method for performinghip replacement surgery in accordance with a first embodiment isgenerally shown at 10. The method 10 is for total hip replacement,namely, with the insertion of an acetabular cup in the acetabulum and ofa femoral implant in the resected femur. The method 10 comprises thesequence of Steps 12 to 17.

Referring to FIG. 3, the femur is schematically identified as A, asbeing positioned with respect to a pelvis B having an acetabulum C.

Referring to FIG. 1, in Step 12, a frame of reference is digitized forthe pelvis. As an example, referring to FIG. 3, a trackable reference 18is secured to the pelvis B, whereby a tracking of the trackablereference 18 provides position and orientation of points, forming aframe of reference. The frame of reference typically has a coordinatesystem with frontal, sagittal and transverse planes, and otherinformation such as a 3D digitization of the acetabulum. In order todigitize the frame of reference, the hip joint is exposed by thesurgeon.

Referring concurrently to FIGS. 1 and 3, in Step 13, the provisional orfemoral implant 19 is inserted into the femur A. Step 13 may involve theresection of the femur A, the alteration (e.g., rasping) of theintramedullary canal of the femur A, and the positioning of theprovisional or femoral implant 19 in the intramedullary canal. Theprovisional refers to any tool or device that is temporarily connectedto the femur so as to simulate the position and orientation of thefemoral implant 19 (e.g., the neck of the implant 19, a trial neck of atool). For instance, the provisional is a rasp or like tool having atrial neck. For simplicity purposes, reference will now be made to thefemoral implant 19, even though reference numeral 19 represents either afemoral implant or a provisional in FIG. 3.

In Step 14, the leg supporting the femoral implant 16 is positioned in aselected position in which the femur A and the pelvis B are in a desiredpostural relation. In an embodiment, the desired posture relation hasthe leg positioned approximately in the regular lying position of thepatient (i.e., this selected position of the leg is used to takemeasurements such as anteversion and offset).

In Step 15, the femoral neck axis D is digitized with respect to theframe of reference of the pelvis (i.e., the trackable reference 18) atthe desired postural relation. As will be described hereinafter, thedigitization is performed by a trackable hip-joint device 20, althoughother alternatives are considered.

In Step 16, a desired position/orientation of the acetabular implant isdetermined from the femoral neck axis D digitized in Step 15. Thedesired position/orientation (i.e., cup implanting information) isselected to minimize the risk of dislocation, and maximize the range ofmovements of the provisional or femoral implant 19 with respect to theacetabular cup, in view of impingement.

In Step 17, the acetabular cup is implanted in the acetabulum C. Thistypically involves the reaming of the acetabulum C to an appropriatesize, and the navigation of the acetabular cup to adjust the orientationof the cup in the reamed acetabulum C to have the cup implanted in thedesired position/orientation as obtained in Step 16. It is pointed outthat the reaming of the acetabulum C may optionally be performed priorto the resection of the femoral implant in Step 13.

Step 18 is performed if a provisional was used in Step 13. With theprovisional removed, the femoral implant is inserted in its desiredposition.

In Step 15, it is desired to digitize the provisional or femoral implantneck D with respect to the pelvic frame of reference. Referring to FIG.2, a trackable hip-joint device 20 is provided therefor. The trackablehip-joint device 20 has a trackable reference 21 that is tracked forposition and orientation. The trackable reference 21 is connected to abody of the device 20, and more precisely to an implant interface 22.The implant interface 22 is shaped so as to connect to the neck of theprovisional or femoral implant 19 in a known manner. A bone interface23, embodied by a ball head, is connected to the implant interface 22.The bone interface 23 is shaped and selected as a function of thedimension of the acetabulum C.

In the embodiment of FIGS. 2 and 3, it is pointed out that bothtrackable references 18 and 21 are illustrated as being of theretro-reflective passive type (e.g., retro-reflective patterns such asspheres or circles in a known geometry), as used with an opticalapparatus. However, other modes of tracking can be used, such as RFtracking, magnetic tracking, accelerometers, gyroscope, etc.

By way of a calibration or of a model provided by a CAS system, an axisD is provided along the implant interface 22 and the bone interface 23.As the implant interface 22 connects to the neck of the provisional orfemoral implant 19 in a known manner, the axis is selected as beingcoincident with the axis D of the femoral neck of the femur A (with theimplant 19).

Moreover, as the bone interface 23 is shaped as a ball head, it isselected in dimension as a function of the diameter of the acetabulum C,the interconnection between the femur and the pelvis is reproduced whenthe device 20 has its ball head accommodated in the acetabulum C and theinterface 22 on the neck of the provisional or femoral implant 19. In anembodiment, the selected position of the leg described in Step 14 hasthe leg positioned preferably in full extension but can also bepositioned with a certain degree of flexion, abduction/adduction orinternal/external rotation to reproduce the position of the leg in themultiple functional positions representative of daily activities.Therefore, with the axis D being digitized at the selected position ofthe leg, the position/orientation data for the acetabular cup is used tocalculate the optimal anteversion, inclination and offset whereby therange of motion of the implanted hip joint is calculable with respect tothe pelvic frame of reference obtained in Step 12.

Alternative steps can be used to digitize the femoral neck axis asdescribed in Step 15. For instance, it is considered to use aregistration tool to digitize surface points on the neck of the implant19 (FIG. 3) when the leg is in a full extension position.

It is observed that a reference anchored to the femur A can be used butis not needed. Therefore, the method 10 described above is not asinvasive as other known CAS THR procedures. Moreover, some THRprocedures require a trackable reference to be secured to the femur nearthe knee. Accordingly, trackable references often require additionalincisions in the soft tissue, and these incisions are not required withthe method 10 described above.

Referring to FIG. 4, a computer-assisted surgery system used to performTHR, for instance using the method 10 described previously, is generallyillustrated.

The computer-assisted surgery system has a sensor apparatus 40 that isprovided to track the reference 18 and the device 20 in space forposition and orientation. As mentioned previously, the sensor apparatus40 may be any of an optical tracking apparatus, an RF trackingapparatus, and a magnetic tracking apparatus, accemelerometer/gyroscopesystems.

The CAS system has a CAS controller 50. The controller 50 is aprocessing unit that receives commands from an operator and providesinformation to the surgeon through interfaces (i.e., screen,touchscreen, mouse, keyboard, etc.). The CAS controller 50 providesinteractive information so as to guide the surgeon in the steps tofollow throughout THR procedures.

A position/orientation calculator 51 is connected to the CAS controller50. The calculator 51 provides position and orientation data pertainingto the pelvic frame of reference and to the trackable device 20 (i.e.,position and orientation of the axis D). A database 52 is provided inconjunction with the CAS controller 50 so as to record digitization datarelated to the frame of reference. For instance, it may be desired todigitize a surface of the acetabulum C, to define planes (e.g., frontal,sagittal, transverse) for the frame of reference, or record the positionand orientation of the femoral implant axis with regard to the pelvicframe of reference. Moreover, a calibration may be performed to obtainthe axis D (FIG. 3) of the device 20. These types of information aretypically recorded with the database 52.

Alternatively, a virtual model of the trackable device 20 may beprovided by the database 53. In such a case, no calibration of thetrackable device 20 is required. The operator identifies the selectedtrackable device 20 to the CAS controller 50, whereby the position ofthe axis D with respect to the trackable reference 21 is calculable bythe position/orientation calculator 51 using the virtual model providedby the database 53.

A cup position and orientation calculator 54 is associated with the CAScontroller 54 and determines a suitable position and orientation for thecup implant. The suitable position and orientation are calculated usingthe projected femoral neck axis as digitized with respect to the pelvicframe of reference. One contemplated way of providing the calculated cupimplanting information is as surgical parameters, such as varyinganteversion angle, offset angle, limb length discrepancy, as a functionof the tracking of the cup implant. Alternatively, the information maybe provided in the form of a range of motion of the hip joint.

The invention claimed is:
 1. A system for calculating a position andorientation of an acetabular cup in computer-assisted surgery,comprising: a first trackable reference adapted to be secured to apelvis, with a frame of reference being associated with the firsttrackable reference; a device adapted to be positioned between a femoralneck and an acetabulum of the pelvis to simultaneously physically lointhe femoral neck to the acetabulum, the device having a second trackablereference; sensors for tracking the first and second trackablereferences; a position/orientation calculator for tracking the frame ofreference of the first trackable reference, and for tracking the device,and for determining an orientation of a neck axis of the femoral neckwith respect to the frame of reference when the device simultaneouslyphysically loins the femoral neck to the acetabulum; and an implantposition/orientation calculator for providing cup implanting informationwith respect to the orientation of said neck axis as a function ofinformation provided by the sensors tracking at least the firsttrackable reference.
 2. The system according to claim 1, furthercomprising a reamer for reaming the acetabulum of the pelvis, the reamerhaving another trackable reference such that the cup implantinginformation is calculated as a function of the orientation of thereamer.
 3. The system according to claim 1, further comprising anothertrackable reference removably connectable to the acetabular cup suchthat the cup implanting information is calculated as a function of theorientation of the acetabular cup.
 4. The system according to claim 1,wherein the device comprises a body connected to the second trackablereference, the body having an interface portion adapted to be releasablycoupled to a neck of an implanted femoral implant or provisional, and abone interface portion adapted to be positioned into the acetabulum suchthat the body of the device interrelates the implanted femoral implantto the pelvis when the device simultaneously physically joins thefemoral neck to the acetabulum.
 5. The system according to claim 1,wherein the cup implanting information comprises at least one ofanteversion angle, offset angle, limb length discrepancy, range ofmotion data, visal displays of an axis with respect to a pelvic image.6. The system according to claim 1, wherein the patient lies in aregular posture when the device simultaneously physically joins thefemoral neck to the acetabulum.
 7. The system according to claim 1,wherein the position/orientation calculator comprises a model of thedevice.
 8. The system according to claim 1, wherein the femoral neck isthe femoral neck of any one of a femoral implant and provisional.